In recent years, for a work machine such as a hydraulic excavator to reduce the throttle components in a hydraulic circuit driving a hydraulic actuator such as a hydraulic cylinder to thereby achieve a reduction in fuel consumption, there is being developed a hydraulic circuit (hereinafter referred to as the closed circuit) in which connection is effected such that the hydraulic working fluid is sent to a hydraulic actuator from a hydraulic drive source such as a hydraulic pump and that the hydraulic working fluid having performed work at the hydraulic actuator is returned to the hydraulic pump instead of returning it to the tank.
JP-1984-208205-A (Patent Document 1) discloses a background-art technique of the present technical field. The above-mentioned publication discloses a flushing valve discharging surplus fluid flow inside a hydraulic closed circuit, in which there are provided a first pressure receiving section connected to the rod side flow line of a single rod cylinder for generating the force for driving a spool selecting the destination of connection and a second pressure receiving section connected to the head side flow line, with the pressure receiving area of the second pressure receiving section being set to be larger than the area of the first pressure receiving section.
Due to the provision of such a flushing valve, even when the pressure balance within the single rod cylinder instantaneously fluctuates, the switching of the flushing valve is stabilized, making it possible to smoothly drive the single rod cylinder.